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| United States Patent |
5,680,765
|
|
Choi
, et al.
|
October 28, 1997
|
Lean direct wall fuel injection method and devices
Abstract
A fuel combustion chamber, and a method of and a nozzle for mixing liquid
fuel and air in the fuel combustion chamber in lean direct injection
combustion for advanced gas turbine engines, including aircraft engines.
Liquid fuel in a form of jet is injected directly into a cylindrical
combustion chamber from the combustion chamber wall surface in a direction
opposite to the direction of the swirling air at an angle of from about
50.degree. to about 60.degree. with respect to a tangential line of the
cylindrical combustion chamber and at a fuel-lean condition, with a liquid
droplet momentum to air momentum ratio in the range of from about 0.05 to
about 0.12. Advanced gas turbines benefit from lean direct wall injection
combustion. The lean direct wall injection technique of the present
invention provides fast, uniform, well-stirred mixing of fuel and air.
| Inventors:
|
Choi; Kyung J. (723 Falcon Dr., Wyndmoor, PA 19038);
Tacina; Robert (4619 Basswood Oval, Brunswick, OH 44212)
|
| Appl. No.:
|
583629 |
| Filed:
|
January 5, 1996 |
| Current U.S. Class: |
60/740; 60/746; 60/776; 239/434 |
| Intern'l Class: |
F02C 001/00 |
| Field of Search: |
60/39.06,740,746
239/439,461
|
References Cited
U.S. Patent Documents
| 1591679 | Jun., 1926 | Hawley.
| |
| 3078672 | Feb., 1963 | Meurer | 60/746.
|
| 3099134 | Jul., 1963 | Calder et al.
| |
| 4257760 | Mar., 1981 | Schuurman et al.
| |
| 4891936 | Jan., 1990 | Shekleton et al.
| |
| 4928479 | May., 1990 | Shekleton et al.
| |
| 4928481 | May., 1990 | Joshi et al.
| |
| 5150570 | Sep., 1992 | Shekleton.
| |
| 5176324 | Jan., 1993 | Furuse et al. | 239/433.
|
| 5205117 | Apr., 1993 | Shekleton et al.
| |
| 5263316 | Nov., 1993 | Shekleton.
| |
| 5479781 | Jan., 1996 | Fric et al.
| |
Other References
N. Ahmad, et al., "Centrifugal Mixing in Gas and Liquid Fuelled Lean Swirl
Stabilised Primary Zones", Int'l Journal of Turbo and Jet Engines 3,
319-329 (Jan. 1986).
N. Ahmad, et al., "Gas and Liquid Fuel Injection into an Enclosed Swirling
Flow", Int'l Journal of Turbo and Jet Engines 3, 331-342 (Jan. 1986).
|
Primary Examiner: Freay; Charles G.
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus, LLP.
Claims
What is claimed is:
1. A fuel injection nozzle for injecting liquid fuel into a combustion
chamber, said fuel injection nozzle comprising an elongated, hollow
cylindrical body member having a first end with an inlet opening for flow
of liquid fuel into said hollow body member, and a second end with a
single outlet opening for injection of liquid fuel as a jet from within
said hollow body member through said outlet opening at an angle of from
about 30.degree. to about 40.degree. with respect to the longitudinal axis
of said elongated body member to thereby inject the liquid fuel into said
combustion chamber in a direction opposite to a direction of air swirling
in said combustion chamber.
2. A liquid fuel combustion apparatus, comprising:
a hollow cylindrical combustion chamber member having a first end and a
cylindrical wall, with a fuel inlet orifice through said cylindrical wall;
an air swirler attached to said combustion chamber member first end and
coaxial with said combustion chamber member, for introducing swirling air
in a predetermined direction into said combustion chamber member, said air
swirler including a hollow annular swirler body with a plurality of
swirler vanes therein, each vane being angled with respect to the axis of
said annular swirler body; and
a fuel injection nozzle including an elongated, hollow cylindrical nozzle
body member having a first end with an inlet opening for flow of liquid
fuel into said nozzle body member, and a second end with a single outlet
opening positioned to inject the liquid fuel as a jet through said nozzle
body member outlet opening and said combustion chamber member fuel inlet
orifice at an angle of from about 50.degree. to about 60.degree. with
respect to a tangential line of the combustion chamber member cylindrical
wall in a direction opposite to the predetermined direction of the
swirling air, to cause the liquid fuel and the air to mix abruptly and
uniformly in a well stirred mixing mode.
3. A liquid fuel combustion apparatus as claimed in claim 2, wherein said
air swirler vanes are angled at an angle of about 45.degree. with respect
to the axis of said annular swirler body.
4. A liquid fuel combustion apparatus as claimed in claim 3, wherein said
combustion chamber member fuel inlet orifice is spaced approximately one
inch longitudinally from said combustion chamber member first end.
5. A liquid fuel combustion apparatus as claimed in claim 2, wherein said
combustion chamber member fuel inlet orifice is spaced approximately one
inch longitudinally from said combustion chamber member first end.
6. A liquid fuel combustion apparatus as claimed in claim 2, wherein said
combustion chamber member has a second fuel inlet orifice and said
apparatus further comprises a second fuel injection nozzle including a
second elongated, hollow cylindrical nozzle body member having a second
nozzle body member first end with an inlet opening for flow of liquid fuel
into said second nozzle body member, and a second nozzle body member
second end with a single outlet opening positioned to inject the liquid
fuel as a jet through said second nozzle body member outlet opening and
said combustion chamber member second fuel inlet orifice at an angle of
from about 50.degree. to about 60.degree. with respect to a second
tangential line of the combustion chamber member cylindrical wall, to
cause the liquid fuel and the air to mix abruptly and uniformly in a well
stirred mixing mode.
7. A liquid fuel combustion apparatus as claimed in claim 6, wherein said
combustion chamber member fuel inlet orifices are spaced approximately one
inch longitudinally from said combustion chamber member first end.
8. A method of injecting liquid fuel into a hollow cylindrical combustion
chamber having a first end and a cylindrical wall, said method comprising
the steps of:
(a) introducing swirling air in a predetermined direction through said
combustion chamber first end into said combustion chamber;
(b) injecting liquid fuel as a jet through said cylindrical wall and into
said hollow cylindrical combustion chamber in a direction opposite to the
direction of the swirling air at an angle of from about 50.degree. to
about 60.degree. with respect to a tangential line of the combustion
chamber member cylindrical wall thereby forming liquid droplets; and
(c) maintaining the ratio of the liquid droplet momentum to air momentum in
the range of from about 0.05 to about 0.12,
whereby the liquid fuel and the air mix abruptly and uniformly in a well
stirred mixing mode.
9. A method as claimed in claim 8, wherein the liquid fuel is injected into
said hollow cylindrical combustion chamber approximately one inch from
said hollow cylindrical combustion chamber first end.
10. A liquid fuel combustion apparatus, comprising:
a hollow cylindrical combustion chamber member having a first end and a
cylindrical wall, with a fuel inlet orifice through said cylindrical wall;
an air swirler attached to said combustion chamber member first end and
coaxial with said combustion chamber member, for introducing swirling air
in a predetermined direction into said combustion chamber member, said air
swirler including a hollow annular swirler body with a plurality of
swirler vanes therein, each vane being angled with respect to the axis of
said annular swirler body; and
one or more fuel injection nozzles including an elongated, hollow
cylindrical nozzle body member having a first end with an inlet opening
for flow of liquid fuel into said nozzle body member, and a second end
with a single outlet opening positioned to inject the liquid fuel as a jet
through said nozzle body member outlet opening and said combustion chamber
member fuel inlet orifice in a direction opposite to the direction of the
swirling air at an angle of from about 50.degree. to about 60.degree. with
respect to a tangential line of the combustion chamber member cylindrical
wall, to cause the liquid fuel and the air to mix abruptly and uniformly
in a well stirred mixing mode to increase combusion efficiency.
Description
BACKGROUND
The present invention relates to lean direct fuel injection combustion.
More particularly, the present invention relates to a fuel combustion
chamber and a method of and a nozzle for mixing of liquid fuel and air in
such chamber, for example in a gas turbine engine, including an aircraft
engine.
Several lean direct fuel injection (LDI) concepts have recently been
considered for advanced gas turbine engine development. Although some of
the concepts have shown acceptable combustion results, the geometrical
configuration of the fuel-air mixers is complicated, and the combustion
results have not been fully satisfactory. Development of new fuel
injectors to be applied to LDI concepts is of great importance in
development of advanced gas turbines. For the past several years,
conventional fuel injectors, such as air-blast atomizers and pressure
atomizers, have been utilized in development of high-performance gas
turbine engines. However, more practical fuel injectors which are less
prone to clogging are needed for future advanced aircraft engines.
Objectives of this invention are to produce rapid and uniform mixing of
liquid fuel and air in combustion zones and to provide high thermal
performance and low emissions in aircraft gas turbine engines. Developing
advanced gas turbine engines for all speed ranges--subsonic, supersonic,
and hypersonic--is one of the most urgent and important areas of
aeronautical research and development. Achieving high thermal efficiency
and low emissions, especially, NO.sub.x, from the gas turbine engines is a
major objective. As a first step to achieving this goal, increase of the
inlet air compression ratio (up to 60 to 1) and fuel-lean burning have
been proposed, leading to the lean direct fuel injection (LDI) concept at
high pressure and temperature. In the LDI concept, combustion performance,
especially emission generation, depends to a great degree upon the quality
of the fuel-air mixing in the combustion zone. Problems that have been
encountered include (1) providing rapid and uniform mixing of lean-fuel
and rich-air in a direct injection mode, (2) improving flame stability
under lean combustion conditions, (3) reducing power loss through the
fuel-air mixing process, and (4) preventing clogging of injector orifices.
Since the LDI concept was introduced to aircraft engine manufacturers, some
preliminary emission tests have been done by agencies of the United States
government, aircraft engine companies, and academic institutions. Such
tests have revealed that the LDI concept has a potential for future
advanced gas turbine engines and that LDI combustion performance depends
to a great degree upon the quality of fuel-air mixing.
In the LDI mode, liquid fuel is directly injected in a fuel lean ratio into
a burning zone which is confined and compact. This injection method is in
reality an extension of the current lean-premixed-prevaporized (LPP)
concept. However, the major difference is that LPP physically separates
the fuel-air mixing process from the combustion process, while LDI does
not. Also, flame stabilizing is built into the fuel-air mixing process,
rather than having a separate flame-holder.
SUMMARY OF THE INVENTION
The present invention is an improved method of rapid and uniform mixing of
liquid fuel and air in lean direct injection (LDI) combustion with minimum
power loss, and a mixing device, including a single swirler and a pressure
fuel injector, which is geometrically simple in structure and easy to
manufacture.
From previous studies of LDI, important factors for successful development
of advanced LDI combustors are known as follows: (1) low pressure drop
through the fuel-air mixer, (2) good flame stability, (3) rapid and
uniform mixing of fuel and air in the combustion zone, and (4) prevention
of clogging of injector tips. As the air operating conditions become more
severe (high pressure and temperature), these factors become more
important.
The first two objectives can be achieved by a single global scale mixing
method, i.e., using a single large air swirler which is located in the
frontal plane of the combustor. For the third objective, a lean direct
wall injection (LDWI) method can be utilized. A few years ago, English
researchers for the first time studied direct wall injection and direct
central injection in confined swirl flow under atmospheric pressure
conditions. They found some improvement in NO.sub.x reduction with the
wall injection of kerosene and propane fuels, but no improvement for gas
oil.
Other research has been done on LDWI, including LDWI flame temperature
tests, results of which are shown in FIG. 1. The results shown in FIG. 1
are from tests conducted at NASA with a 2.5 GPH P-H nozzle as can be seen
there, overall emission was off the target value; however, the LDWI test
results show an interesting feature, i.e., as the adiabatic flame
temperature (or fuel-air equivalence ratio .o slashed.) increases, the
NO.sub.x emission level decreases, which is contradictory to accepted
knowledge. For conventional gas turbine combustors, it is accepted that an
increase of the fuel-air ratio will generate more NO.sub.x. The test
results were rearranged in terms of emission index and applied injector
pressure and are presented in FIG. 2. It is clearly shown that the
emission level decreases as the injector pressure increases at any fixed
air mass flow rate.
Cold flow visualization tests of LDWI have provided very interesting
observations about the LDWI concept, i.e., satisfactory liquid spray-air
mixing depends to a great extent on the relative motion of the liquid
spray with respect to the swirling air. In other words, better mixing of
liquid spray can be achieved where the liquid droplet momentum is
sufficiently large to penetrate the swirling air flow.
FIG. 3 shows results of water spray mixing in a confined air swirl flow,
where the water spray was injected from the wall surface using a pressure
injector and the conditions are equivalent to the test conditions used for
the results depicted in FIG. 2, except for the air pressure and
temperature. Specifically, FIG. 3 shows LDWI mixing using a
Parker-Haniffin Nozzle at 200 psia (m.sub.c =2.9 g(s), incident to swirl
nozzle plane; 1". It can clearly be seen in FIG. 3 that most liquid
droplets injected from the combustor wall do not fully penetrate the air
stream; instead, they impact on the nearby wall surface. As the injector
pressure increases, more liquid droplets stay in the air flow, resulting
in better mixing. This is a reason why the increased injector pressure
produced a lower NO.sub.x level as shown in FIG. 2.
Two factors have been found to be very important for the LDWI technique to
be successful: (1) the ratio of the liquid droplet momentum to the
swirling air momentum, and (2) the angle at which the liquid jet
encounters the swirling air flow. The liquid droplet momentum should be
large enough to overcome the upcoming swirling air momentum so that the
liquid droplets can penetrate into the core region of the air flow, but
the liquid droplet momentum should not be so large that the liquid
droplets directly impact on the opposite wall of the combustor. Thus, the
ratio of the liquid droplet momentum to the air momentum should be at an
optimum value. It was discovered that the optimum value for the test
conditions described below was in the range of from about 0.05 to about
0.12 and depends on the nozzle orifice size.
It was also found that in order to get an optimum ratio of droplet momentum
to air momentum, using a liquid jet is better than using a pre-atomized
liquid spray. From recent observation, it has also been found that the
liquid jet should come out at a predetermined angle with respect to the
tangential line of the circular tube. Injection of liquid jets at an
inclined angle is essential for a successful LDWI combustor.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects and advantages of the present invention are more
apparent from the following detailed description and claims, particularly
when considered in conjunction with the accompanying drawings. In the
drawings:
FIGS. 1 and 2 are graphs presenting test data related to the making of the
present invention;
FIG. 3 depicts a test conducted during the making of the present invention;
FIG. 4 is a sectional view of a pressure injector in accordance with a
preferred embodiment of the present invention;
FIGS. 5A and 5B are schematic representations of lean direct wall injection
in accordance with a preferred embodiment of the present invention, with
FIG. 5B being taken along line X--X of FIG. 5A;
FIGS. 6A-6C are cross-sectional views of an air swirler suitable for use in
a lean direct wall injection system in accordance with the present
invention, with FIG. 6B being taken along line Y--Y of FIG. 6A and FIG. 6C
showing the configuration of a vane of the swirler; and
FIGS. 7A to 7F, 8A, 8B and 9A to 9C depict the test results of the present
invention and comparisons of results with other cases.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The presently preferred embodiment of the present invention is a new type
of injector, in the form of a simple pressure injector nozzle with a
single hole or orifice at a predetermined inclined angle, which is much
simpler than conventional air-blast or pressure nozzles used in current
aircraft engines. FIG. 4 depicts an injector nozzle 20 utilized in tests
of the present invention. Injector nozzle 20 has a single orifice 22 at
the tip 24 of the injector nozzle. The axis 26 of orifice 22 is positioned
at an angle .o slashed. with respect to the longitudinal axis 28 of the
injector nozzle 20, and so at an angle .theta. with respect to the normal
to that longitudinal axis, as shown in FIG. 4. Consequently, nozzle 20
injects a single jet of liquid at such angle. Having a single orifice 22
in the injector body, without any insert inside the injector nozzle 20,
makes this injector very practical for advanced aircraft engines,
especially under severe operating conditions. The nozzle 20 utilized in
the tests had a length of 1.452", an external diameter of 0.300", and an
internal diameter of 0.125". The size of the end orifice 22 is variable,
and the thickness of the body at the end orifice can be set as 0.0625",
for example.
The present invention provides an improved method of rapid and uniform
mixing of liquid fuel and air in lean direct injection (LDI) combustion
with minimum power loss. The mixing method includes the following: (1)
liquid fuel is directly injected into a combustor in a lean-fuel mode
(so-called, Lean Direct Injection), (2) liquid fuel is injected in the
form of a jet from the combustor walls (so called, Wall Injection), and
(3) the liquid jet is injected at an inclined angle .theta., preferably in
a range of from about 50.degree. to about 60.degree., with respect to the
tangential line of the cylindrical combustor wall, as depicted in FIG. 5B.
The combined characteristics of this concept result in it being referred
to as Lean Direct Wall Injection (LDWI) and result in it being very unique
and completely different from both conventional aircraft fuel injection
concepts and other currently developing LDI concepts.
In tests of fuel-air mixing utilizing such an injector, a chamber in the
form of a transparent cylindrical tube 28 as depicted in FIG. 5A, having a
diameter of 3.0 inches, was used. Two injector nozzles 20 were utilized.
The air was introduced through air swirler 32. To design an air swirler
which creates maximum recirculating zones in both the front core and the
corner regions of the circular flame tube, numerical analysis was used to
obtain dimensions as shown in FIGS. 6A-6C. The vane angle of the swirler
is 45.degree., and the twelve vanes are preferably evenly spaced. Liquid
water was injected in several different ways using different fuel injector
orifice sizes. By way of example, the swirler in FIGS. 6A-6C can be
constructed to have an external diameter of 2.325", an internal diameter
of 1.44", a wall thickness of 1/16", a vane thickness of 1/32" and a depth
of 3/4".
Test results of fuel-air mixing are presented in FIGS. 7-9. FIGS. 7A-7F
depicts central injection, and FIGS. 8 and 9 depict lean direct wall
injection (LDWI). The results are for a constant air flow rate of 73.0 g/s
at atmospheric pressure and temperature. FIGS. 7A-7F show the results of
liquid spray mixing at different axial locations where the liquid spray
was injected in the axial direction through a center portion of the
swirler. As shown in FIGS. 7A-7F, droplet mixing does not take place in a
well-stirred fashion; instead, the droplet distribution is not uniform in
the space, and it takes time for the droplets to distribute in a certain
space. FIGS. 7A-7F illustrate mixing using a Textron Injector. In FIGS.
7A-7C, Pj=100 psia (m.sub.1 =3.7 g/s). In FIGS. 7D-7F, Pj=150 psia (m1=4.4
g/s).
FIGS. 8A and 8B show shows the results of droplet mixing at the injector
tip for single liquid jet injection, where the liquid jet is injected
normal to the tube axial direction, i.e., in FIG. 4 .theta.=90.degree.,
the injection being from the tube wall at an axial distance x; of 1.0"
from the swirler (where m.sub.1 =1.9 g/s and m.sub.a =73.0 g/s. In this
wall injection case, there is no significant improvement in mixing;
instead, most droplets impact upon either the opposite wall surface or the
nearby wall surface, depending on the ratio of the liquid droplet momentum
to the air flow momentum. As the liquid droplet momentum becomes small
relative to the air momentum, the penetration of liquid droplets into the
air flow decreases, and most droplets impact on the nearby wall surface.
FIGS. 9A to 9C show shows results of single liquid jet mixing where the jet
was injected from the wall surface with an inclined angle .theta. of
60.degree., as depicted in FIGS. 5A and 5B (where x.sub.j =1", m.sub.1
=2.3 g/s and m.sub.a =73.0 g/s). As shown in these photos, LDWI with
inclined angle .theta.=60.degree. results in very remarkable uniform and
quick mixing of droplets. The basic reason for the superiority of the LDWI
technique is thought to be that the liquid jet injected from the side wall
of the combustor immediately encounters the swirling airflow, resulting in
very fast atomization of the liquid jet and vigorous mixing of the liquid
spray with the air flow. This vigorous mixing is increased due to the
liquid jet being injected at an angle .theta. with respect to the
tangential line of the cylindrical tube 30, based on the arrangement of
the axis 26 of the orifice 22 at an angle .o slashed. with respect to the
longitudinal axis 28 of the injector nozzle 20. When the angle .theta. is
between about 50.degree. and about 60.degree., and thus the angle .o
slashed. between about 30.degree. and about 40.degree., the mixing
performance is best. Also, as mentioned above, with the equipment used in
this test when the ratio of the liquid jet momentum to the air flow
momentum is in the range of from about 0.05 to about 0.12, the best mixing
takes place. An injector in accordance with the present invention, having
an orifice diameter of 0.45 mm, was used for the test.
It was observed that wall injection of a liquid jet provides an advantage
over pre-atomized spray wall injection in that a liquid jet is naturally
atomized by encountering the swirling air flow without the need for a
complicated atomizing device. Therefore, it is advantageous to use raw
liquid jets for the LDWI method. It was also observed that at the current
air flow conditions the liquid flow rates for best mixing were in the
range of 4.05 to 5.25 g/s. For other ranges of liquid flow rate, different
orifice sizes are needed for optimum mixing performance. In application to
aircraft gas turbine engines, different numbers of fuel injectors which
have an optimum orifice size compatible with the actual operating
conditions may be implemented to vary the fuel-air equivalence ratio. The
use of this technique is very simple and reliable, yet produces
well-stirred mixing of liquid fuel and air. Repeatability of this
technique has been well verified by testing.
Data on droplet size distribution were approximated using a visualization
technique, and it was observed that the droplet size seemed slightly
larger than with conventional mixing techniques. However, it is thought
that the combustion performance, especially NO.sub.x production, of
advanced aircraft gas turbine engines, depends greatly on the droplet
number density distribution rather than on the droplet size distribution
in flame zones, because vaporization of the fuel droplets under severe
operating conditions (such as critical and super-critical) will take place
in a flash mode due to an extremely low surface tension of the liquid
fuels. If this is correct, then smaller droplet size may produce poorer
combustion performance. It is understood that recent tests have resulted
in an unorthodox finding on NO.sub.x production, i.e., increased droplet
size reduced NO.sub.x emissions. In addition, general combustion
characteristics under such severe environmental conditions are much
different from what is generally understood due to non-ideal gas effects,
gas phase solubility, boundary layer stripping, and combustion
instability. However, uniform mixing and uniform distribution of liquid
droplets in lean direct combustion have been determined to promote lower
NO.sub.x emissions.
Novel and unique features of this lean direct wall injection (LDWI)
technique include: (1) low pressure drop of the air is experienced through
the fuel-air mixing process, (2) liquid fuel-air mixing takes place
abruptly and uniformly, i.e., in a well-stirred mixing mode, (3) a minimum
number of fuel injectors are required to obtain a satisfactory degree of
fuel-air mixing, and (4) the geometrical configuration is relatively
simple and, therefore, practical to apply to advanced gas turbine engines.
The first two features above are very important in regard to the advanced
gas turbine program, because achieving high thermal performance and low
NO.sub.x emission are main objectives of the program. Usually large scale
mixing by using a single large swirler is preferable in view of pressure
drop; however, the quality of fuel-air mixing is poor in general. The
present technique satisfies both requirements, i.e., low pressure drop and
good liquid droplet distribution. The third and fourth features above are
also important in view of engineering applications to gas turbine engines.
With regard to the third feature, although the number of injectors used in
general varies depending on the characteristics of the engine being used,
it is expected that, in each case, the number of injectors of the present
invention will be less than the number of conventional injectors that
would be required in the same engine.
Along with this novel LDWI technology, the present invention includes the
simple and practical fuel injector of FIG. 4. The preferred embodiment of
the fuel injector of the present invention has the following unique
features: (1) a liquid jet comes out through a single orifice on the
injector tip at an inclined angle .theta. of 50.degree. to 60.degree. with
respect to the tangential line of the circular combustor wall, (2) the
fuel injector contains only one simple orifice at the tip, without any
other complicated inserts, and (3) geometrical configuration and
fabrication of the injector are much simpler than presently available
air-blast or pressure injectors which are used in current aircraft
engines. In most existing gas turbine combustors, fuel sprays are
generated through complicated inner components of fuel injectors. The
major advantages of the present injector are that it is simple to use and
inexpensive to fabricate. In addition, this injector avoids clogging of
the injector tip, which would be a serious problem in fuel injectors used
under high temperature conditions, such as encountered in advanced
aircraft gas turbine engines. Further, the injector of the present
invention avoids clogging problems since it can be fabricated in the
simple way shown in FIG. 4, with a single large orifice at the injector
tip and without any complicated inserts.
Although the invention has been described with respect to a preferred
embodiment, it is to be understood that modifications of this embodiment
could be made without departing from the scope of the invention. For
example, the injector itself could be modified in terms of angles, orifice
size and shape, geometrical configuration and arrangement along the wall
while still accomplishing the goals of the present invention.
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